Poly(propylene carbonate), old CO2 Copolymer with New Attractiveness

Summary: The catalytic synthesis of poly(propylene carbonate) (PPC) from propylene oxide and CO2 is mediated by zinc glutarate and chromium salen complexes. The determined solid state structure of the zinc glutarate was taken to model the polymerisation of ethylene oxide. It has a low activation energy for a reaction path involving two zinc atoms, where one binds the nucleophilic alkoxy chain end and one activates the epoxide. A similar pathway may operate in the alternating copolymerization PO/CO2 as is shown in the homogeneous chromium salen catalyst system. The material profile was determined of PPC with 93% carbonate linkages. A study of the transparent blend with poly(lactic acid) (PLA) shows that the polymers are not miscible, but rather compatible as they are finely dispersed and show linear behaviour in the mechanic properties. The permeability of oxygen, carbon dioxide and water of the composite PPC/PLA are also reported.